The present invention relates to a method and apparatus for polishing a semiconductor substrate whereby chemical mechanical polishing (CMP) is performed with respect to a semiconductor substrate of silicon or the like to flatten a surface thereof.
From the 1990s, CMP technology for polishing semiconductor substrates of silicon or the like has shown increasing tendencies toward single-wafer processing as the semiconductor substrates processed by CMP have had larger diameters on the order of 10 cm or more, resulting in an increased amount of slurry consumed per wafer.
By way of example, a conventional apparatus for polishing a semiconductor substrate will be described below with reference to the drawings.
FIG. 22 schematically shows the construction of the conventional polishing apparatus, in which is shown a platen 11 including: a substrate holder 11a made of a rigid material and having a flat surface; a rotary shaft 11b extending vertically downwardly from the back surface of the substrate holder 11a; and rotating means (not shown) for rotating the rotary shaft 11b. To the top surface of the substrate holder 11a of the platen 11 is adhered a polishing pad 12. Above the platen 11 is provided a substrate holding head 14 which holds and rotates a semiconductor substrate 13. The semiconductor substrate 13 is rotated and pressed against the polishing pad 12 on the platen 11 by the substrate holding head 14. A slurry 15 containing abrasive grains (extremely fine powder for polishing) is dropped in a prescribed amount from a slurry supply pipe 16 onto the polishing pad 12 so as to supply the abrasive grains to the space between the polishing pad 12 and the semiconductor substrate 13.
In the polishing apparatus thus constructed, the polishing pad 12 supplied with the slurry 15 is rotated by rotating the platen 11 and the semiconductor substrate 13 is pressed against the rotating polishing pad 12 by the substrate holding head 14 so that a surface of the semiconductor substrate 13 is polished.
In this process, if the surface of the semiconductor substrate 13 is rugged, the polishing rate is increased at projecting portions of the semiconductor substrate 13 since their contact pressure with the polishing pad 12 is high. On the other hand, the polishing rate is reduced at recessed portions of the semiconductor substrate 13 since their contact pressure with the polishing pad 12 is low. Consequently, the surface of the semiconductor substrate 13 becomes less rugged and more smooth.
However, the above polishing apparatus have the following problems.
When a consideration is given to the amount of supplied slurry and the polishing rate, the polishing rate increases with increases in the amount of supplied slurry 15 and eventually becomes constant when the amount of supplied slurry reaches a given value. Accordingly, the amount of slurry 15 normally supplied onto the polishing pad 12 is slightly larger than the given value with which the polishing rate becomes constant.
However, since the slurry 15 is supplied onto the rotating polishing pad 12 as described above, the slurry 15 is caused to flow to the peripheral portion of the polishing pad 12 by a centrifugal force accompanying the rotation of the platen 11. When the amount of slurry 15 becomes smaller than the given value, the polishing rate is reduced. To compensate for the reduction in the polishing rate, the pressure for pressing the semiconductor substrate 13 against the polishing pad 12 should be increased. However, the increased pressure induces dishing or like phenomenon, which causes such a problem as the degradation of polishing properties. Hence, the slurry should constantly be supplied in an amount slightly larger than the given value with which the polishing rate becomes constant, so that the cost of the slurry accounts for a considerable proportion of the cost of polishing.
To solve the problem, there have been proposed an apparatus and method for polishing wherein a slurry on a polishing pad is prevented from flowing out by a partition board enclosing the polishing pad, as disclosed in U.S. Pat. No. 4,910,155.
According to the apparatus and method for polishing, however, foreign matters such as tips of polishing pad generated at the polishing are accumulated on the polishing pad. Also, water supplied onto the polishing pad to clean up a semiconductor substrate after polishing or perform dressing (the conditioning of the surface of the polishing pad) as well as the slurry is prevented from flowing out, resulting in unfavorable variations in the concentration of the slurry, which changes the polishing properties.